Equilibrium and Dynamics of Polymer-Grafted Nanoparticles at Fluid Interfaces

1332836PI：Tilton聚合物刷子是一种被戏称为聚合物链的单层，每个聚合物链的一端固定在一个表面上，而链的其余部分从表面延伸到溶剂中。此前，由该团队支持的研究开发了聚合物刷装饰纳米颗粒，这些纳米颗粒是水包油或油包水乳状液的极其有效的稳定剂。这些纳米粒子刷稳定乳状液数月至一年以上，没有乳状液液滴聚合或宏观油水相分离。最重要的是，他们这样做的同时，只需要纳米颗粒的浓度比用于稳定乳剂的常规颗粒通常所需的浓度低两个数量级。拟议研究的目标是确定导致纳米颗粒刷子独特乳化效率的基本界面现象。目前对颗粒稳定的Pickering乳液的理解主要涉及长期稳定性的起源，但它还不能解释为什么具有不同物理化学性质的颗粒产生的乳液具有非常相似的长期稳定性，但乳化效率却有很大的差异，也就是为什么它们首先需要非常不同的浓度才能产生稳定的乳液。这就需要对纳米颗粒吸附到油/水界面时的界面性质进行基础研究。指导这项研究的主要假设是，那些在最低表面浓度下产生最强界面张力降低和界面弹性的纳米粒子刷子将是最有效的乳化剂。通过可控自由基聚合法合成了一系列成分和结构明确的纳米刷子。对于每个纳米粒子刷，将在油/水界面测量表面状态方程(界面张力与被吸附粒子表面浓度之间的关系)、界面膨胀弹性和扩散动力学，并与乳化效率相关联。纳米刷子是一种新型的表面活性材料。通常，这种材料的设计目的是操纵不兼容材料之间的界面，使它们更兼容。例如，它们将油和水混合在乳剂中，从而在药品或个人护理产品中提供有效成分。这项研究具有变革性，因为它专注于纳米粒子刷子是极其高效的乳化剂的根本原因，并将为更广泛的基础理解提供化学结构如何控制这类新的表面活性材料的界面行为。这一知识将使具有超低乳化剂浓度的高稳定性乳液产品成为可能。除了高效利用原材料的好处外，这也保证了新产品在没有乳化剂的情况下是不可行的，既高效又高效。一种可能性是一种清洁燃烧的柴油乳状液，它可以满足严格的稳定性要求，而不需要过量的添加剂。化学工程和化学博士和本科生的跨学科研究教育对技术劳动力发展产生了更广泛的影响。来自代表性不足群体的匹兹堡中学生将在密切相关的、以发现为基础的科学项目中接受指导，这些项目教会学生如何使用科学理解来进行预测？在这种情况下，涉及到不同种类材料的界面张力降低和乳化性能。与高中化学学生的研讨会访问将介绍与化学相关的全部职业，以鼓励他们在过渡到大学时保留在STEM途径中。这项研究由CBET(化学、生物、环境和运输)工程部的颗粒和多相过程以及界面过程和热力学项目共同资助。

1332836PI: TiltonA polymer brush is a descriptively named monolayer of polymer chains, each of which is anchored by one end to a surface, while the rest of the chain stretches away from the surface into a solvent. Prior NSF-supported research by this group developed polymer brush-decorated nanoparticles that were extremely efficient stabilizers of oil-in-water or water-in-oil emulsions. These nanoparticle brushes stabilized emulsions for several months to well over a year without emulsion droplet coalescence or macroscopic oil and water phase separation. Most importantly, they did so while only requiring nanoparticle concentrations that were two orders of magnitude lower than are generally required for conventional particles used to stabilize emulsions. The goal of the proposed research is to determine the fundamental interfacial phenomena responsible for the unique emulsifying efficiency of nanoparticle brushes. Current understanding of particle-stabilized Pickering emulsions mainly concerns the origins of long-term stability, but it cannot yet explain why particles with different physico-chemical properties produce emulsions with quite similar long-term stability yet display vastly different emulsifying efficiencies, that is, why they require vastly different concentrations to produce a stable emulsion in the first place. This requires fundamental investigation of the interfacial properties of the nanoparticles when they adsorb to the oil/water interface. The main hypothesis guiding this research is that those nanoparticle brushes that produce the strongest interfacial tension reduction and interfacial elasticity at the lowest surface concentration will be the most efficient emulsifiers. A series of nanoparticle brushes with well-defined compositions and architectures will be synthesized by controlled radical polymerization. For each nanoparticle brush, the surface equation of state (the relationship between interfacial tension and the adsorbed particle surface concentration), interfacial dilatational elasticity, and diffusional dynamics will be measured at the oil/water interface and correlated with emulsifying efficiency. Nanoparticle brushes are a new class of surface active material. Typically, such materials are designed to manipulate the interface between incompatible materials to make them more compatible. For example, they mix oil and water in emulsions that deliver active ingredients in pharmaceuticals or personal care products. This research is transformative for its focus on the fundamental reasons why nanoparticle brushes are extremely efficient emulsifiers and for the broader fundamental understanding it will provide for how chemical structure controls the interfacial behavior of this new class of surface active materials. This knowledge will enable high stability emulsion products with ultra-low emulsifier concentrations. Besides the benefit of efficient raw materials usage, this also promises new products that are infeasible without emulsifiers that are both highly effective and highly efficient. One possibility is a clean-burning diesel fuel emulsion that meets stringent stability requirements without excessive additives. Broader impact for technology workforce development is delivered by the interdisciplinary research education of Chemical Engineering and Chemistry Ph.D. and undergraduate students. Pittsburgh middle school students from under-represented groups will be mentored in closely-related, discovery-based science projects that teach students how they can use scientific understanding to make predictions ? in this case concerning interfacial tension reduction and emulsification performance of different kinds of materials. Seminar visits with high school chemistry students will introduce the full spectrum of chemistry-related careers to encourage retention in the STEM pathway as they transition to college.This reasearch is jointly funded by the Particulate and Multiphase Processes and Interfacial Processes and Thermodynamics Programs in the CBET (Chemical, Biological, Environmental and Transport) division in Engineering.